This invention is directed to an electron beam system where the system is capable of selectively producing either a small round electron beam spot on a target or a larger square electron beam spot on the target. When used for electron beam lithography, the small spot is used for exposing fine pattern structures and the larger square electron spot is for exposing larger areas.
When writing with an electron beam on a target, such as exposing photolithographic sensitive material, a small beam size is capable of writing fine structures, but takes a long time to fill-in large areas. Conversely, if a large electron beam is used, large areas can be rapidly filled-in but fine structures cannot be detailed. A previously known method provides a completely variable square or rectangular spot size. However, this requires an extremely complex electron-optical system as well as complex computer software. This is described by Pfeiffer "Variable Spot Shaping for Electron Beam Lithography"Fourteenth Symposium on Electron, Ion and Photon Beam Technology, May 1977. Another system produces only a fixed size square probe and is not suitable for exposing structures requiring finest detail. This system is described in the IBM Journal of Research and Development, November 1977, pages 498-521.